1) Melt half the butter in a large pan and fry the onion until soft, then add the rice and stir thoroughly until opaque and sizzling.
2) Add the wine and allow it to evaporate for 1-2 minutes.
3) Add in a ladle of stock. Over a medium heat, keep stirring until the liquid has all been absorbed, then continue to add the hot stock a ladleful at a time.
4) When the rice is cooked, add the rocket, cream, remaining butter and Parmesan.
5) Season to taste, stir again and cover. Leave to rest for 2 minutes before serving.